day2 solution

src/day02.rs

@@ -0,0 +1,61 @@
+use crate::utils::read_file;
+use anyhow::Result;
+
+fn parse_line(s: &str) -> (&str, i32) {
+    let parsed: Vec<&str> = s.splitn(2, ' ').collect();
+    let instruction = parsed[0];
+    let quantity = parsed[1].parse::<i32>().unwrap();
+    (instruction, quantity)
+}
+
+fn follow_course(s: &str) -> i32 {
+    let (mut pos, mut depth) = (0, 0);
+    s.lines().for_each(|line| match parse_line(line) {
+        ("forward", d) => pos += d,
+        ("down", d) => depth += d,
+        ("up", d) => depth -= d,
+        _ => unreachable!(),
+    });
+    pos * depth
+}
+
+fn follow_course_better(s: &str) -> i32 {
+    let (mut pos, mut depth, mut aim) = (0, 0, 0);
+    s.lines().for_each(|line| match parse_line(line) {
+        ("forward", d) => {
+            pos += d;
+            depth += aim * d;
+        }
+        ("down", d) => aim += d,
+        ("up", d) => aim -= d,
+        _ => unreachable!(),
+    });
+    pos * depth
+}
+
+pub(crate) fn run() -> Result<(usize, usize)> {
+    let input = read_file("data/day02.txt")?;
+    Ok((
+        follow_course(&input) as usize,
+        follow_course_better(&input) as usize,
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        let input = read_file("data/day02-test.txt").unwrap();
+        assert_eq!(follow_course(&input), 150);
+        assert_eq!(follow_course_better(&input), 900);
+    }
+
+    #[test]
+    fn test_my_data() {
+        let input = read_file("data/day02.txt").unwrap();
+        assert_eq!(follow_course(&input), 2070300);
+        assert_eq!(follow_course_better(&input), 2078985210);
+    }
+}

src/main.rs

@@ -1,9 +1,11 @@
 use anyhow::Result;
 
 mod day01;
+mod day02;
 mod utils;
 
 fn main() -> Result<()> {
     println!("day01: {:?}", day01::run()?);
+    println!("day02: {:?}", day02::run()?);
     Ok(())
 }